The rapid progress of ink jet recording technology has made it possible to form high-quality colored images on recording media such as paper and films with printers utilizing the ink jet recording technology (hereinafter, referred to as “ink jet printers”). Such ink jet printers range from small home printers to large format printers. Because these printers basically perform printing on a single sheet basis, they have been mainly utilized at printing worksites handling small numbers of copies. The printing speed of large format printers is several meters or less per minute, although variable depending on the printing size or the image quality.
As a result of further progress in the technology, ink jet recording has recently become used in industrial printing (hereinafter, referred to as “ink jet printing”). Because large numbers of copies are printed in the industrial printing field, printing speed is important due to the productivity and the printing costs. A printing speed suitable for ink jet printing is achieved with a printing machine that is equipped with a line head in which ink-ejecting heads are fixed in the entirety of the width direction perpendicular to the paper transport direction (hereinafter, such a printing machine will be referred to as “ink jet printing machine”) (see, for example, Patent Literature 1). More recently, rotary ink jet printing machines using pigment inks have been developed which have a printing speed of 15 m/min or more, a higher speed of 60 m/min or more, and a still higher speed in excess of 120 m/min.
Because ink jet printing machines allow for handling of variable information, their use is particularly found in on-demand printing. A preferred manner of industrial printing is to print fixed information with an offset printing machine and to print variable information with an ink jet printing machine.
However, poor fixation and absorption of ink jet inks are encountered when conventional coated offset printing paper is used in printing with an ink jet printing machine at such a printing speed as described above. As a result, the printed image is smeared by abrasion caused during post-printing handling. Further, because the absorption of inks is insufficient, printing at the above printing speed results in problems such as the occurrence of uneven printing, blurred printing and, in the worst cases, ink bleeding (a phenomenon in which an ink that has remained unabsorbed bleeds on the coated paper).
Ink fixing properties and ink absorption properties during ink jet printing may be improved by simply reducing the amount of a binder in a coating layer or by adding a large amount of a porous pigment to a coating layer. However, such approaches result in the occurrence of problems such as blanket piling to cause a decrease in the coating strength of the coating layer, thereby deteriorating the offset printability of the coated printing paper.
From the viewpoint of weather resistance, ink jet printing machines tend to be configured to be loaded with ink jet pigment inks. Problems encountered with pigment inks include uneven printing in printed sections. Uneven printing is a phenomenon in which coated printing paper exhibits a nonuniform density of an ink fixed in the printed image after the ink is dried to cause uneven ink absorption properties during high speed printing. Because inks used in ink jet printing have a low concentration of color material, uneven printing tends to be more marked than in offset printing. The presence of uneven printing deteriorates the commercial value of prints.
Exclusive paper for ink jet recording in which base paper is coated with a porous pigment having a high BET specific surface area (see, for example, Patent Literatures 2 and 3) exhibits excellent ink fixing properties and ink absorption properties during ink jet printing. However, such ink jet recording exclusive paper is poor in offset printability due to insufficient strength of the coating layer.
Further, ink jet recording exclusive paper which suppresses the occurrence of uneven printing in printed images has been developed. Such recording media are ink jet recording sheets which include support paper containing a water-soluble metal salt, and an ink receiving layer containing a protein on the support paper (see, for example, Patent Literature 4); ink jet recording paper which has an ink receiving layer and a gloss layer on a support wherein the gloss layer contains 5 to 30 wt % of a chloride of a Group 2A element in the periodic table (see, for example, Patent Literature 5); and ink jet recording paper which has an ink receiving layer and a gloss layer on a substrate and is further provided with an overcoating layer containing a multivalent metal salt and a penetrating agent (see, for example, Patent Literature 6). However, these types of ink jet recording exclusive paper are dedicated to ink jet printers. Thus, they are poorly suitable for offset printing, and cannot suppress the occurrence of uneven printing to a sufficiently satisfactory level when used for ink jet printing machines. Other types of ink jet recording paper have been disclosed in which base paper containing a cationic polymer is coated with a coating layer based on an inorganic pigment and a binder (see, for example, Patent Literature 7). Such recording paper exhibits good offset printability but is often rather unsatisfactory in terms of uneven printing when used for ink jet printing machines.